1. Field of the Invention
The present invention relates in general to a solenoid valve, and more particularly to improvements in or relating to a solenoid valve which is most suitable for use in an anti-lock braking system.
2. Description of the Prior Art
In general, it is known that, with the use of an anti-lock braking system in a passenger carrying vehicle which operates at a relatively high speed, the rotating velocity of the vehicle wheels is detected by way of a revolution velocity sensor, and the thus obtained speed data is electronically differentiated to provide a wheel acceleration signal at an electronic control section. In accordance with this wheel acceleration signal, there is determined a sign or transient symptom of a tendency of a wheel or wheels of the vehicle to become locked when the brakes are applied during cruising of the vehicle at a relatively high speed. Upon such determination, a suitable operating command is given to a modulator or hydraulic regulating mechanism, so that a suitable counter operation to ensure maneuverability or operating stability of the vehicle may be taken quickly, and braking force is applied in such a manner that the vehicle wheels are allowed to slip to an appropriate extent, so that the vehicle may positively be stopped within the shortest possible braking distance.
In such a typical construction of the anti-lock braking system as stated above, it is generally known that there is incorporated a certain control means such as a pair of normally-opening and normally-closed solenoid valves, each of which solenoid valves is adapted to be opened or closed individually for the purpose of regulating the hydraulic brake force by providing a hydraulic pressure modulator with a hydraulic brake regulating pressure or by relieving this hydraulic regulating pressure to a hydraulic pressure reservoir.
The present invention relates to the provision of a solution to the maintenance and security of the proper hydraulic braking pressure regulation of the hydraulic pressure modulator or pressure regulating mechanism in the hydraulic braking system as experienced in the conventional hydraulic braking system.